1. Field of the Invention
The present invention relates to a rocking switch which rocks forward from its neutral position to a first rocking position and back from the neutral position to a second rocking position and outputs predetermined switching signals at the respective rocking positions.
2. Description of the Related Art
In a known structure of rocking movement-activated switches, a main body itself is supported by a rocking shaft in the manner that allows free rocking movements of the main body. This structure restricts the rocking movements to one direction in order to realize only one type of switching operation for a fixed purpose. As long as this conventional structure is applied, separate switches are required to realize two different types of switching operations for two different purposes. The separate switches, however, undesirably increase the required space.
An improved structure proposed to save the space allows only one switch to realize two different types of switching operations for two different purposes. A tilt and telescopic switch mounted on a vehicle is given as a typical example of the switches of such improved structure. The tilt and telescopic switch is used to vary the angle of inclination of a steering wheel and change the axial position of the steering wheel according to the physical constitution or requirements of a driver. The tilt and telescopic switch implements the tilt switching for varying the angle of inclination based on rocking movements in a first direction and the telescopic switching for changing the axial position based on rocking movements in a second direction, which is different from the first direction.
As shown in the cross sectional view of FIG. 10, a conventional tilt and telescopic switch 50 includes a switch casing 16 assembled by fitting a lower casing member 14 into a lower opening of an upper casing member 12, and a main body 18 received and accommodated in the space defined by the switch casing 16. The main body 18 has a knob fixing member 22, which is projected upright through an upper opening 20 formed in the upper casing member 12. A control knob 24 is fixed to the knob fixing member 22 by means of a pin 26.
The main body 18 includes a first hemispherical member 28 on the side close to the control knob 24 and a second hemispherical member 30 on the side away from the control knob 24. The second hemispherical member 30 is disposed on the lower end of the main body 18 and concentrically arranged with the first hemispherical member 28. The knob fixing member 22 is integrally joined with the outer top portion of the first hemispherical member 28, whereas the second hemispherical member 30 is joined with the inner top portion of the first hemispherical member 28.
A plane ring 32 is formed as a rim of the lower opening of the first hemispherical member 28. Four pressure projections 34a, 34b, 34c, and 34d are arranged at the equal pitches on the lower face of the plane ring 32. Only the two pressure projections 34a and 34b are shown in FIG. 10 and the other pressure projections 34c and 34d (not shown) are located in front of and behind the sheet surface of FIG. 10. Four switching elements 36a, 36b, 36c, and 36d are disposed on the upper face of the lower casing member 14 at positions corresponding to those of the four pressure projections 34a, 34b, 34c, and 34d so as to face the respective pressure projections 34a through 34d. Only the two switching elements 36a and 36b are shown in FIG. 10 and the other switching elements 36c and 36d (not shown) are located in front of and behind the sheet surface of FIG. 10. The switching elements 36a through 36d output switching signals when downward pressure is applied to the respective upper faces of the switching elements 36a through 36d by means of the pressure projections 34a through 34d formed on the lower face of the plane ring 32.
The upper casing member 12 has a first hemispherical recess 38 formed to define the opening 20. The outer radius of the first hemispherical member 28 of the main body 18 is substantially equal to the inner radius of the first hemispherical recess 38. The lower casing member 14 has a second hemispherical recess 40, which faces the opening 20 and the first hemispherical recess 38 of the upper casing member 12. The second hemispherical recess 40 is arranged concentrically with the first hemispherical recess 38 and combined with the second hemispherical member 30 of the main body 18 to define a clearance therebetween.
A chamber 41 formed in the center of the second hemispherical member 30 of the main body 18 receives a touch piece 42 and a spring 44 for pressing the touch piece 42. The touch piece 42 is freely movable toward and away from the second hemispherical recess 40 of the lower casing member 14. A spot facing hole 45 and a through hole 46 are formed on the center of the lower end of the second hemispherical recess 40. The lower end of the touch piece 42 comes into contact and engagement with the spot facing hole 45.
The main body 18 accommodated in the switch casing 16 continuously receives the pressing force of the spring 44. The first hemispherical member 28 of the main body 18 accordingly comes into contact with the first hemispherical recess 38 over the substantially whole hemispherical surface thereof and is guided by the hemispherical inner surface of the first hemispherical recess 38. This rocks the main body 18 back and forth either in the direction shown by the double-headed arrow X or in the direction perpendicular to the direction X. The second hemispherical member 30 of the main body 18, on the other hand, is received by the second hemispherical recess 40 while not being in direct contact with or guided by the second hemispherical recess 40. The direct contact of the second hemispherical member 30 with the substantially whole hemispherical inner surface of the second hemispherical recess 40 increases the contact resistance in the rocking movements of the main body 18, thus requiring a relatively large force for operations of the control knob 24. In the structure of the embodiment, the radius of the second hemispherical recess 40 is set a little greater than the radius of the second hemispherical member 30. This ensures a clearance between the second hemispherical member 30 and the second hemispherical recess 40 and prevents the second hemispherical member 30 from being in direct contact with the second hemispherical recess 40.
In the conventional switch thus constructed, although only the first hemispherical member 28 of the main body 18 is guided by the first hemispherical recess 38, there are some cases in which a relatively large force is required for operations of the control knob. This is attributable to the following.
The respective elements of the tilt and telescopic switch 50 are generally made of resin because of its light weight advantage and excellent forming properties. The shapes and dimensions of the respective elements are determined in the process of design. For example, the outer radius of the first hemispherical member 28 of the main body 18 is set substantially equal to the inner radius of the first hemispherical recess 38 of the upper casing member 12. The radius of the second hemispherical recess 40 of the lower casing member 14 is set a little greater than the radius of the second hemispherical member 30 of the main body 18. The inner diameter of the chamber 41 formed in the center of the second hemispherical member 30 is designed to be a little greater than the dimensions of the touch piece 42, in order to allow the touch piece 42 to be freely movable in the chamber 41 toward and away from the second hemispherical recess 40. Namely there is a little clearance between the wall of the chamber 41 and the touch piece 42.
Although the first hemispherical member 28 is designed to have the outer radius substantially equal to the inner radius of the first hemispherical recess 38, the inner radius of the first hemispherical recess 38 should be a little greater than the outer radius of the first hemispherical member 28 to allow the first hemispherical member 28 to be guided by the first hemispherical recess 38. When the control knob 24 is operated in the direction of the arrow X0 shown in FIG. 10, only the main body 18 rocks until the touch piece 42 comes into contact with the wall of the chamber 41. The slight difference between the outer radius of the first hemispherical member 28 and the inner radius of the first hemispherical recess 38 prevents the first hemispherical member 28 from being completely in contact with the first hemispherical recess 38 over the whole surface thereof. This may cause the main body 18 to be guided and rocked by only one side of the first hemispherical recess 38, for example, by a hemispherical portion A shown in FIG. 10. The one-sided guide results in a deviation of the center of the rocking movement of the main body 18 from the center of the hemispherical surface of the first hemispherical member 28.
The deviation of the rocking center brings the first hemispherical member 28 of the main body 18 into contact with the hemispherical portion A of the first hemispherical recess 38 and makes the main body 18 rock about the hemispherical portion A. This results in a clearance at another hemispherical portion B on the other side of the first hemispherical recess 38. A hemispherical portion C of the second hemispherical member 30 apart from the second hemispherical recess 40 thus comes into contact with the hemispherical inner surface of the second hemispherical recess 40. Irrespective of the clearance formed between the second hemispherical member 30 and the second hemispherical recess 40 to prevent a direct contact, the second hemispherical member 30 comes into contact with the second hemispherical recess 40. This may undesirably increase the force required for the operation of the control knob 24.
The sliding properties of the hemispherical inner surface of the second hemispherical recess 40 may be enhanced by applying a lubricant or improving the spherical precision. Such measures, however, do not radically settle the above problem since adhesion of dust and shrink or sink marks of the resin in the molding process are inevitable. Increasing the clearance between the second hemispherical member 30 and the second hemispherical recess 40 is not advantageous, because the increased clearance does not meet the favorable arrangement of the switching elements 36a through 36d on the upper face of the lower casing member 14, the demands for thin-walled switches, and the sufficient strength of the lower spherical recess 40. The highly precise control of dimensions of the respective elements is required to determine the minimum clearance which does not induce the above problem. This requires the thorough quality control in the manufacturing process and additional equipment for realizing the highly precise control of dimensions, thereby increasing the labor and cost.